I don't think supporting obsolete hardware should be the deciding factor regarding which option you use, unless you explicitly have that need.
I guess that I wasn't clear or I kind of mixed my points, sorry about that.
On one hand ffmpeg's dialog is just that: use "this option" to maximize compatibility; I wanted to let you know (case you hadn't seen it).
On the other hand that dialog also gives us the change needed to assure 8bit output regardless of source's colour bit deph. I strive to hit a balance between small size, IQ and playability (hillbilly cousin). For previews and light copies a x264 420 8bit works 4 me. Most computers read it without hiccups and - as you mentioned - only the trained eye ( with a good enough screen) can tell the diff.
/// amend \\
As you and @patdavid mentioned x265, you can pack a lot in the same bag but it can also be tricky to deliver copies in x265 as some clients ( we talking mostly rodents) might not be able to play them. That said I often upload 10bit x265 files to vimeo, sometimes also to youtube (less frequent as in YT there's no filesize limit) and I always keep and deliver the masters in proRes 422 HQ.
Thank you and thanks pataD =)
@Andrius the libfdk_aac incompability was solved by brew compiling ffmpeg
BTW I also tried you script and works perfectly and output is just _x264 =) It has too many parts though